1. Technical Field of the Invention
The present invention relates to novel compounds comprising short-chain, linear or cyclic diorganosiloxanes or triorganosilanes bearing at least one sunscreening cinnamonitrile substituent bonded thereto via an alkylene or alkyleneoxy bridging group.
This invention also relates to novel cosmetic compositions for topical application comprising said cinnamonitrile-substituted polyorganosiloxanes/polyorganosilanes, for the photoprotection of the skin and/or hair against ultraviolet radiation (such compositions hereinafter sometimes simply designated "sunscreen," "sunscreen/cosmetic" or "photoprotective/sunscreen" compositions).
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths of from 280 to 320 nm, i.e, UV-B irradiation, causes erythema and skin burns which can impair the development of a natural tan; hence, such UV-B radiation must thus be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths of from 320 to 400 nm, which tans the skin, also adversely affects it, in particular in the event of sensitive skin or skin constantly exposed to solar radiation. UV-A irradiation causes, in particular, a loss in the elasticity of the skin and the appearance of wrinkles, promoting a premature aging thereof. Such irradiation promotes triggering of the erythematous reaction or enhances this reaction in certain individuals, and may even be the source of phototoxic or photoallergic reactions. Thus, it is desirable to also screen out UV-A radiation.
A wide variety of compounds intended for the photoprotection (UV-A and/or UV-B) of human skin are known to this art.
Most of these are aromatic compounds displaying an absorption of UV radiation in the region from 280 to 315 nm or in the region of from 315 to 400 nm, or else in both of these regions together. They are, more often than not, formulated in sunscreen compositions as oil-in-water emulsions (namely, a cosmetically acceptable vehicle, carrier or diluent comprising an aqueous continuous dispersing phase and an oily discontinuous dispersed phase) which contain, at various concentrations, one or more traditional lipophilic and/or hydrophilic organic sunscreen compounds comprising an aromatic function suitable for selectively absorbing harmful or deleterious UV radiation. These sunscreen compounds (and the amounts thereof) are selected as a function of the desired specific sun protection factor (the specific protection factor (SPF) being expressed mathematically by the ratio of the irradiation time required to attain the erythemogenic threshold with the UV screening agent to the time required to attain the erythemogenic threshold in the absence of UV screening agent.)
Other than their sunscreen activity, these compounds having anti-UV properties must also display good cosmetic characteristics in the compositions comprised thereof, good solubility in common solvents, and especially fats such as oils and greases, and also good resistance to water and to perspiration (durability). It too is desirable that these sunscreen compositions be nontoxic and do not penetrate into the skin.
Among such prior art aromatic compounds, p-aminobenzoic acid derivatives, benzylidenecamphor derivatives, cinnamic acid derivatives and benzotriazole derivatives are particularly representative. However, certain of these, as well as others of the known sunscreen compounds do not display all of the properties required for an acceptable UV screening agent in sunscreen compositions. In particular, their intrinsic screening activity may be insufficient, ofttimes mandating that relatively large amounts of compound be employed to attain satisfactory screening properties, but at the expense of the cosmetic properties of the ultimate formulations thereof. In addition, their solubility in the different formulations employed for photoprotection is not always sufficiently good (fat solubility in particular), they may not possess sufficient stability to light (photostability) and they may also display poor resistance to water and to sweat.